Non Explosion Proof

M2A Series Non Explosion Category

The RKI M2A™ is a state-of-the-art transmitter that can operate as an independent, stand-alone monitor or as part of an integrated system. The M2A connects with an analog or digital signal to virtually any controller, PLC, or DCS. Setup procedures are simplified with user friendly push buttons and OLED menus. It utilizes a magnetic wand technique for performing non-intrusive calibration. The M2A provides an automatic zero drift correction feature, which results in more stable readings and reduces the need for adjustments due to sensor aging.

The housing of the M2A does not need to be opened for zeroing or calibration, making it unnecessary to declassify the area for routine maintenance. It is designed so that a complete field calibration can be performed by one person. Sensor construction is rated Class I, Div. 1 Groups B, C, D for flammables, CO, H2S, O2, and CO2, and Class I, Div. 2 for all other toxics.

The transmitter provides a 4-20 mA output in addition to a Modbus digital output. It also has two levels of alarms with relays, plus a fail alarm with relay. A digital display of the gas concentration, as well as alarm and status lights, can be viewed through the front window.

The toxic sensors are electrochemical type plug-in sensors, which provide high specificity, fast response, and long life. The plug-in design allows quick replacement in the field with no tools required. Toxic sensors are designed for use in Class I, Div. 2 hazardous locations. Sensors available for NH3, SO2, PH3, AsH3, and HCN.

The M2A represents the latest leading edge technology in sensor / transmitters today.

  • Operates with or without a controller
  • Direct digital readout with OLED cold temperature display
  • LEL, O2, H2S, CO, CO2,
    • 100% Vol CH4, and 0-9,000 PPM CH4
    • Toxic Gases include NH3, SO2, HCN, and more
  • Infrared sensor for combustibles and CO2
  • 4-20 mA & digital Modbus outputs standard
  • 2 fully programmable alarm relays & fail relay
  • Non-intrusive calibration via magnetic wand
  • Explosion proof construction
  • Patented water repellent sensor cover
  • User friendly setup, push buttons & OLED menus
  • Long-life sensors (2+ years typical)
  • Petrochemical plants
  • Refineries
  • Water & wastewater treatment plants
  • Pulp & paper mills
  • Manufacturing facilities
  • Automotive
  • Semiconductor plants
  • Chemical plants




Hydrogen Sulfide


Carbon Monoxide


See Chart Below


Carbon Dioxide






See Chart Below






Galvanic cell



Measuring Ranges

0-25% Vol.

0-100 ppm

0-300 ppm

See Chart Below


0 – 5000 ppm



0 – 5% Vol.

0 – 50% Vol.


0 – 100% Vol.


0.1% Vol.

1 ppm

See Chart Below

20 ppm / 0.01% Vol. / 0.1% Vol. / 1%Vol.

Lower Detectable Limit (LDL)

0.1% Vol.

2% of full scale

Response Time (T-90)

35 Seconds or less

60 Seconds or less

30 Seconds or less

Max Current Draw (24VDC)

125 mA with alarm 1 and alarm 2 active and all relays energized

160 mA with alarm 1 and alarm 2 active and all relays energized

Life Expectancy

2 to 3 years with normal service

5 years plus

Accuracy (which ever is greater)

± 0.5% Vol. O2

± 5% of reading or ± 2 ppm H2S

± 5% of reading or ± 5 ppm CO

± 10% of reading or ± 5% of full scale

± 5% of reading or ± 2% of full scale

Alarm Settings Two fully programmable alarm set points, increasing / decreasing, latching / self-resetting, on delays, off delays, normally energized or de-energized,
Alarm Indication Visual LEDs. Alarm 1=Amber; Alarm 2=Red; Fail=Red
Relays 5 Amp form ‘C’ contacts for alarm 1, alarm 2, and fail
Dimensions Height: 8.5” (215 mm), Width: 5.2” (132 mm), Depth: 4.5” (114 mm)
Display Alphanumeric OLED display. 8 characters per line; 2 lines for gas concentration readout, plus user-friendly calibration and setup
Sensor Rating Non explosion proof construction, designed for Class I, Div. 2, Groups B, C, D (no certification)
Housing J-Box NEMA 4X, explosion proof, watertight, cast aluminum with o-ring seal and epoxy powder coating
Controls Magnet used for calibration functions. Calibrates without opening the housing. Internal push-button controls also available for calibration and setup
Sensor Aluminum / Plastic (non explosion proof)
Operating Environment
Operating Temperature

-4°F to 113°F -20°C to 45°C

-40°F to 104°F

-40°C to 40°C

23°F to 104°F

-5°C to 40°C

14°F to 104°F -10°C to 40°C

-40°F to 122°F -40°C to 50°C

Relative Humidity 5 – 95% RH non-condensing
Location Indoor or outdoor
Operating Voltage 10 VDC – 30 VDC
Analog Linear 4-20 mA signal, into 1000 ohms impedance max (24DC), 0 – 500 ohms max (12VDC) corresponding to 0 – full scale
Digital Modbus RTU output standard, fully configurable, 2-wire RS-485, 1200 to 19.2k baud
Controllers Beacon 110, Beacon 200, Beacon 410A, Beacon 800 as well as most DCS / PLC systems
Warranty One year materials and workmanship

M2A Non Explosion Proof Toxic Transmitter Sensor Ordering Information

Part Number With J-Box Gas Range Resolution Sensor Type
65-2648RK-NH3 Ammonia (NH3) 0 – 75.0 ppm 0.1 ppm ESM -01
65-2648RK-AsH3 Arsine (AsH3) 0 – 1.50 ppm 0.1 ppm ESM -01
65-2670RK-CL2 Chlorine (Cl2) 0 – 3.00 ppm 0.01 ppm CT-7
65-2670RK-CL210 Chlorine (Cl2) 0 – 10.0 ppm 0.1 ppm CT-7
65-2670RK-CLO2 Chlorine Dioxide (ClO2) 0 – 1.00 ppm 0.01 ppm CT-7
65-2648RK-HCN Hydrogen Cyanide (HCN) 0 – 15.0 ppm 0.1 ppm ESM -01
65-2648RK-PH3 Phosphine (PH3) 0 – 1.00 ppm 0.01 ppm ESM -01
65-2648RK-SO2 Sulfur Dioxide (SO2) 0 – 6.00 ppm 0.01 ppm ESM -01